What mistake was Mahadev talking about?

Mahadev told Gauri that Karthikeya and someone else made a mistake. What do you think that means?

That will be shown this coming Sat; after Mahakali saving Karthikeya she would tell him how Mahadev made her realize abt her mistake;
I still think She might hv done any mistake.
Not sure though just guessing 😆

We will know about it next week
I have no idea at all